"We want people to reduce oil purchases to zero, but in certain cases if people can't do that overnight, we'll consider exceptions," Mnuchin told reporters on Friday, clarifying some U.S. officials' comments that there would be no exemptions. Mnuchin's comments were embargoed for release on Monday as other U.S. officials were expected to begin talks in India this week on cutbacks in Iranian oil supplies.

Mnuchin spoke to reporters while en route from Mexico, where he was part of a high-level U.S. delegation led by Secretary of State Mike Pompeo to meet Mexico's next president, Andres Manuel Lopez Obrador.

The Trump administration is pushing countries to cut all imports of Iranian oil from November, when the United States reimposes sanctions against Tehran. Trump withdrew from the multi-national 2015 Iran nuclear deal against the advice of allies in Europe and elsewhere.

A delegation from the U.S. State Department and U.S. Treasury are expected for talks in Delhi this week to discuss Iran sanctions, according to Indian officials. U.S. crude oil exports to India hit a record in June as Indian refiners moved to replace supplies from Iran and Venezuela.